Electric hot plate



July 15, 1941. J. A. KNIGHT 2,249,476

ELECTRIC HOT PLATE Filed Sept. 26, 1958 Patented July 15, 1941 UNiTE STATES ATENT ()FFFWE.

ELECTRIC HOT PLATE .1 ohm A. Knight, Hamilton, Ontario, Canada Application September 26, 1938, Serial No. 231,630

2 Claims.

This invention relates to electric heating devices, and in particular to hot plates such as are used in electric ranges.

One object of my invention is to produce a heating unit with a maximum radiating efliciency of its heating element. A further object is to so construct the hot plate as toenable any vessel regardless of the shape of its bottom to be supported in good heat-absorbing relationship to the radiating element.

I attain my object by means of the following constructions hereinafter more specifically described and illustrated in the accompanying drawing. 7

According to my invention I provide a supporting or carrying disk of refractory insulating material, in the face of which a groove or grooves are formed as is common in the art. In the walls of this groove are formed shoulders whichare equidistant from the upper edges of the walls which form the groove.

Upon these shoulders is supported the wire electric resistance element which is formed with closely set zig-zag bends or undulations and is referred to in the specification as a uniplane element since its thickness is substantially that of the wire of which it is formed. This uniplane element is held in place on the shoulders by means of projected lugs or bosses formed on the groove walls. It must be noted that the construction and form of this resistance element is of great importance as hereinafter described.

In the preferred construction the upper face of the refractory disk takes a concave or inverted conical form and, as the supporting shoulders are equidistant from the upper edges of the walls forming the grooves, the uniplane element itself will be held in a concave or inverted conical position.

The constructions are more fully described and are illustrated in the accompanying drawing in which Fig. 1 is a plan view of an electric hot plate made in accordance with my invention;

Fig. 2 a cross section of the same on the lines 2-2 in Fig. 1;

Fig. 3 plan view on a larger scale of part of the uniplane element; and

Fig. 4 a cross section of part of the same.

In the drawing like letters of reference indicate corresponding parts in the different figures.

Referring to the drawing, l is a refractory disc of known material and in the main of known form. In the upper face of this disc are formed the grooves 2, above the bottoms of which grooves are formed the shoulders 3 on the sides of the walls of the grooves. These shoulders are equidistant from the upper edges of the said walls at all points in the length of the grooves. Projecting lugs or bosses are formed on the said walls above the shoulders to retain the resistance element in position on the shoulders.

The resistance element 5 is bent into zig-Zag form, its total thickness being substantially no greater than the diameter of the wire of which it is formed. It is thus possible to keep all parts of the resistance wire in very close proximity to the upper surface of the disc I, which gives very effective radiation. Further the spacing of the wire above the bottom of the groove materially reduces the effect of the downward radiation, thus decreasing the heating effect on the disc and increasing that on a pot sitting on the disc. The success of this element depends also on the parts of the element lying in close proximity to one another, as only by this means is it possible to provide room for sufficient length of the right size of resistance wire to insure the desired wattage. If a smaller size Wire is used and a shorter length which would be necessary to provide the same wattage, the life of the element will be greatly shortened.

With known means of bending wire it has been found impossible to produce an element in which the bends or undulations are in sumciently close proximity to each other to obtain the desired results, and it was found necessary to devise special machinery for this purpose. My experiments have resulted in the production of a machine which makes it possible to form an element with the undulations even closer together than the thickness of the wire, whereby an element of 1880 watts capacity can be made and installed in a refractory disc having 7%" outside diameter. Such an element in operation will run at a lower temperature and have a longer life than elements of the same capacity helically wound and supported in a similarly refractory disc of the same diameter.

I have found that the best results are obtained when the spacing of the adjacent parts of the uniplane element are not materially greater than the diameter of the wire itself. In fact, the spacing is preferably less than one and one-quarter times the diameter of the wire, which spacing has not heretofore, as far as the applicant is aware, been attained.

The second. important feature of my construction is the formation of the refractory supporting disc, which is of a dished or concaved shape.

The distance between the under surface of the disc and a plane touched by its rim progressively increasing towards the centre of the disc. This insures that the bottom of a cooking utensil placed on the device will be supported so that its entire surface will be in intimate relation to the upper surface of the disc even though the bottom of the utensil may have become convexly distorted in use.

As the shoulders and retaining lugs are equally spaced from the upper edge of the walls forming the grooves, the resistance element is in similar dished relationship to the plane touched by the rim of the refractory disc and thereby is maintained in a position of high heat radiating efficiency with respect to said utensil.

What I claim as my invention is:

1. An electric hot plate of the open type comprising a grooved refractory disc; a uniplane resistance element positioned in the groove and formed of a Zig-zag wire; shoulders formed on the walls of the groove above its bottom on which the edges of the element rest to hold it in spaced relation to the bottom of the groove; and lugs on said walls adapted to hold down the edge of said element, whereby the uniplane resistance element is supported and retained with substantially its entire upper surface in close and unobstructed heat radiating relation to the bottom of a vessel to be heated and positioned on the device, the upper surface of the refractory disc being dished so that it follows a concave surface of revolution.

2. An electric hot plate of the open type comprising a grooved refractory disc; a uniplane resistance element positioned in the groove and formed of a zig-zag wire; shoulders formed on the walls of the groove above its bottom on which the edges of the element rest to hold it in spaced relation to the bottom of the groove; and lugs on said walls adapted to hold down the edge of said element, whereby the uniplane resistance element is supported and retained with substantially its entire upper surface in close and unobstructed heat radiating relation to the bottom of a vessel to be heated and positioned on the device, the upper surface of the refractory disc being dished so that it follows a concave surface of revolution, the resistance element being similarly concavely positioned in the refractory disc.

JOHN A. KNIGHT. 

